Electronic mail, or “e-mail,” has become an increasingly popular form of communication over computer networks, such as the Internet. E-mail allows a user (the sender) connected to a network, to send messages almost instantaneously to another user or multiple users (the recipient(s)) connected to the same network. Because the transfer of information is almost in “real time,” e-mail has become an indispensable tool for many companies to conduct legitimate business over the Internet. However, some businesses have found that they can advertise their products and services by generating and sending mass, unsolicited e-mails, commonly known in the Internet community as “SPAM.” Because these mass e-mails are unsolicited, the recipients consider them a nuisance, because they occupy valuable storage space on the e-mail servers that would otherwise be used to store important e-mails. Furthermore, due to the shear number of unsolicited e-mails that are sent, they can impair or even stop the transmission of legitimate e-mails by overwhelming e-mail servers. For example, a recipient may not be able to receive legitimate e-mails because the storage capacity of the e-mail server that the recipient is connected to may be so overwhelmed with unsolicited e-mails that it may have to reject legitimate incoming e-mail.
Even if the e-mail server is not fully occupied with unsolicited e-mails, the recipient's Internet appliances may be overwhelmed by these junk e-mails. For example, many recipients have Internet-enabled devices such as cellular telephones, personal digital assistants (“PDA”), and pagers that have a limited storage capacity. When a recipient accesses his or her e-mail from one of these devices, the e-mail server downloads the e-mail messages from the recipient's account to these devices. If the recipient's email account contains a large number of SPAM messages, these e-mails can tie up these devices with useless information and deprive the user of valuable resources. The recipient then must waste valuable time deleting these unsolicited e-mails.
E-mail SPAM lists are typically generated by scanning Usenet postings, stealing Internet mailing lists, or searching Internet Web sites for mailing lists. Typically, e-mail SPAM cost the recipient a great deal of money. The recipient must dial-into his or her Internet Service Provider (ISP) to access and download his or her e-mail messages. The recipient therefore, has to pay for the time spent downloading their e-mail messages. If the account is full of unsolicited e-mails, the recipient has to pay to download these messages. Additionally, SPAM costs money for the ISPs to transmit the unsolicited e-mail, which are then passed directly onto the recipients.
One variant of SPAM, known as “foreign SPAM,” however, is particularly troublesome. Foreign SPAM occurs when an unsolicited e-mail message is sent to the mail server of an ISP from a user connected to a foreign network access server (NAS). The “spammer” gains access to the mail server when a “roaming” customer of the ISP is connected to their mail server via the foreign NAS. Once the roaming customer logs onto the NAS as a registered user, he or she is provided an IP address by the foreign NAS to use to connect to the mail server at the ISP. Unfortunately, once the connection is made between the foreign NAS and the ISP, the ISP allows any valid IP address at the foreign NAS to be a valid IP address for accessing the mail server. Thus, anybody currently logged onto the foreign NAS has access to the local ISP mail server. This connection allows a “spammer” to use the ISP's mail servers for distribution of large unsolicited e-mails directly to anyone on the Internet with a valid e-mail address. Because every IP address assigned by the foreign NAS is a valid address for sending mail to the local ISP and a new IP address is assigned during the login process, it is difficult to isolate and block the IP address used by the spammer. Even if the local ISP could block the IP address used by the spammer, the spammer could simply log onto the NAS again, this time with a different IP address and continue to SPAM the mail server. The typical way in which to block the unsolicited e-mail messages is to block all incoming messages originating from the foreign NAS, or account. Although this will prevent the distribution of SPAM, it will also unfortunately prevent access to the mail server by the ISP's roaming customer.
Several methods have been devised to block SPAM. One method used to filter SPAM messages uses SPAM probe e-mail addresses that are planted at various sites within ISP network. The mailboxes corresponding to the SPAM probe e-mail addresses are monitored by a controller. Upon receipt of an e-mail message to the SPAM probe addresses, the controller identifies the source of the e-mail message sent to the SPAM probe and generates an alert signal that also contains a filter function. The alert message is sent to all network servers on the network and the filter function is installed on each server to block all e-mail messages sent from the identified source. The filter function automatically blocks all e-mail (both SPAM and non-SPAM messages) originating from the SPAM source. If a registered user was logged onto the SPAM source as a “roaming” user, the roaming user's access to his or her mail server would be blocked once the filter function for that particular SPAM source was installed.
Another method for blocking SPAM messages involves the use of a Simplified Mail Transfer Protocol (SMTP) authentication. SMTP is the main protocol used to transmit mail from an originating address to a destination address. SMTP includes provisions that require an originating user to enter a password to initiate the transmission of an e-mail message. Unfortunately, not all user-based e-mail applications support SMTP. Those e-mail systems that do support SMTP, typically not utilize the password option. Therefore, introduction of this type of security option would cause two undesirable effects: the sender would have to reconfigure his or her user-based e-mail application to accommodate the change in protocol, and the e-mail application would have to be able to support the protocol. If the user's e-mail application was one that did not support the protocol, then the user would have to switch to one that did support the protocol in order to be able to send e-mail messages while roaming.
Although each of these methods are capable of blocking unwanted SPAM messages, neither method is capable of blocking SPAM messages from a foreign NAS while allowing a roaming customer logged on to the foreign NAS to have unfettered access to his or her mail account. Thus there is a need in the art for a method of blocking foreign SPAM messages while allowing a roaming customer to freely access their e-mail account via a foreign NAS.